1. Field of the Invention
This invention relates to a potentiometric method and apparatus for determining quantitatively hydrogen peroxide concentration and, more specifically, in a preferred form, it relates to a means for determining glucose concentration through hydrogen peroxide analysis in a potentiometric manner.
2. Description of the Prior Art
A number of methods for determining hydrogen peroxide concentrations in various solutions have been known.
Among the known methods are the titrimetric methods using permanganate, ceric ion or iodometry. Of this group, the permanganate method has generally been considered the most accurate. A difficulty with this approach is the fact that the presence of certain interfering compounds which react with permanganate can interfere with the results. Included within the classes of interfering compounds are large quantities of halides, oxalate, aldehydes, salicylic acid and glycerine.
Gasometric analysis, which involves the measurement of evolved oxygen from the decomposition of hydrogen peroxide, has also been known.
Colorimetric methods may be based upon the reaction of hydrogen peroxide to form a colored peroxy compound, the oxidation of reduced dyes or metal-organic complexes, or the reduction of ferricyanide.
It has also been known to employ electrometric methods which are based on the polarographic technic. Hydrogen peroxide is reduced at a dropping mercury electrode at minus 1.2 V against a saturated calomel electrode. The reduced current is used as the indicator for hydrogen peroxide concentration in a solution.
It has also been known to employ various physical methods such as measuring the refractive index of the density of the solution. This can also be accomplished through ultraviolet spectrophotometry.
A number of these approaches as well as others are disclosed in patents and technical literature.
U.S. Pat. No. 3,838,033 discloses an enzyme electrode system which is amperometric in nature and relies on the use of a chemical reagent to serve as an acceptor in the enzymatic reaction. The use of redox dyes as acceptors is disclosed.
U.S. Pat. No. 3,595,755 also discloses a system wherein a chemical reagent is employed as an acceptor. Glucose determination is made as a result of hydrogen peroxide detected after interaction between glucose oxidase and galactose in the presence of iodide.
U.S. Pat. No. 3,770,607 discloses glucose determination apparatus wherein quinone is employed as an enzyme acceptor.
U.S. Pat. No. 3,539,455 discloses enzymes converting a polarographically inactive material into an active material. This system is an amperimetric system. Glucose oxidase is employed to convert glucose into gluconic acid and hydrogen peroxide. The use of a platinum electrode and a semi-permeable membrane are also disclosed.
Various methods of securing enzymes to supports have been disclosed. U.S. Pat. Nos. 3,841,971; 3,839,154 and 3,556,945 relate generally to measurement of changes in electrical conductivity as a result of enzymatic reaction in connection with glucose-glucose oxidase reactions. The use of adsorption, absorption, ion exchange, and covalent bonding are among the means of immobilization discussed. U.S. Pat. No. 3,666,733 discloses the use of acrylamide polymers to which enzymes are attached. See also U.S. Pat. No. 3,788,950 which discloses a system which requires the use of two identical or calibrated oxygen sensors and operates on the measurement of oxygen consumption principal. See also U.S. Pat. No. 3,542,662.
U.S. Pat. No. 3,838,011 relates to a system which measures oxygen produced or consumed.
U.S. Pat. No. 4,024,042 relates to an enzyme electrode with primary emphasis being directed toward such an electrode wherein the essential parts can be sterilized in an autoclave.
U.S. Pat. No. 2,850,359 relates to a unit for testing glucose and is primarily adapted to test for the presence of glucose in urine. The presence and amount of glucose are said to be indicated by color changes in a chromogenic oxygen acceptor.
U.S. Pat. No. 3,403,081 is directed primarily toward a gas detector adapted to be used in detecting poisonous gases and other elements. The reference electrode is said to be made of silver-silver chloride material and the sensor may be made from material such as platinum, nickel or carbon.
There remains, therefore, a need for a hydrogen peroxide quantitative detector which is economical to manufacture and use, provides very accurate readings and is adapted for miniaturization. There is further lacking such a system which is designed to provide potentiometric readout related to the hydrogen peroxide concentration.